Nanotubes are well known structures exhibiting useful structural, electrical, thermal, and other properties presently of interest in a wide variety of technology areas. Nanotubes may exhibit a variety of intrinsic conductivity states. Most fabrication techniques used to grow or deposit nanotubes produce a mixture of single-wall nanotubes (SW-NT) and multiwall nanotubes (MW-NT). Fabrication techniques may also produce nanotubes of varying diameter. Further, fabrication techniques may produce a variety of chiralities (zigzag, armchair, and chiral). In addition to their composition and perhaps other physical properties, the listed characteristics can influence whether a nanotube is “metallic” (that is, conductive), semiconductive, or insulative. For single-wall carbon nanotubes, armchair varieties are typically metallic, chiral varieties are typically semiconductive, and zigzag varieties are typically semiconductive, but may exhibit a small band gap and so can be termed “quasimetallic.”
For some applications, the electrical properties of nanotubes may be of small consequence. However, for other applications, providing nanotubes exhibiting a particular range of conductivity may be essential. The difficulty in sorting nanotubes according to their electrical properties and/or controlling fabrication methods to produce selected electrical properties remains a major challenge in producing nanotubes and in using nanotubes in certain applications. In the area of electronic devices, nanotubes may be suitable as a dielectric for passive elements (e.g., capacitors), as switches, as interconnects, as channel regions in field effect transistors, as field emitters, etc., wherein absence of a particular electrical property may disqualify a nanotube for use.
Due to their mechanical strength, nanotubes have been proposed for use as fillers in concrete and other structural materials. Although at first not appearing to constitute a significant factor, nanotube conductivity might also play some role in achieving the properties desired in applications that do not involve electronic devices. As one possibility, conductivity might be indicative of structural properties such as diameter, chirality, number of walls, etc. and thus indirectly indicate desirable structural properties.
Despite the wide variety of techniques known for producing nanotubes, a desire exists to more efficiently sort nanotubes and/or to control electrical properties during fabrication.